The Islamic State video apparently shows a British jihadist executing James Foley (Picture: Reuters)

Experts will analyse whether the jihadist who executed a journalist in Iraq yesterday is British, the foreign secretary has confirmed.

The fighter who beheaded James Foley appeared to speak with ‘traces of a London accent’ in the YouTube clip. Intelligence services are now piecing together evidence to identify the killer.

Philip Hammond stressed that the Islamic State video has not been verified, but ‘all the hallmarks point to it being genuine’. But the FBI, in conjunction with Mr Foley’s family, believes that the video is authentic, according to GlobalPost.

Mr Hammond added that Britain would send troops to Baghdad to fight the ‘evil organisation’ and oppose Isis ‘with every breath on our body’ as well as claiming the group was waging war on the west.

David Cameron has called off his holiday and returned to Downing Street and will hold meetings today over the ‘shocking and depraved’ killing.

Nations around the world have also joined in the condemnation of the Islamic State. France called Mr Foley’s death a ‘cowardly assassination’, with Barack Obama expected to make a statement at the White House later today.

Mr Hammond said the possible involvement of a Briton in this killing is a reminder of how extremists could return from the Middle East to launch terrorist attacks at home.

He told the BBC: ‘This is a poison, a cancer, what’s going on in Iraq and Syria, and it risks spreading to other parts of the international community and affecting us all directly.

‘We are absolutely aware that there are significant numbers of British nationals involved in terrible crimes, probably in the commission of atrocities, making jihad with IS and other extremist organisations.’

Mr Foley, from New Hampshire, was a freelance journalist with Agence France-Press and GlobalPost. He had been missing in Syria since November 2012.

His mother, Diane, wrote on Facebook: ‘We have never been prouder of our son Jim. He gave his life trying to expose the world to the suffering of the Syrian people.

‘We implore the kidnappers to spare the lives of the remaining hostages. Like Jim, they are innocents. They have no control over American government policy in Iraq, Syria, or anywhere else in the world.’

Mr Foley’s mother, Diane, said the journalist ‘gave his life trying to expose the suffering of the Syrian people’ (Picture: AP)

The YouTube video of Mr Foley’s execution, which has since been taken down, appears to have been professionally recorded. He is shown wearing an orange jumpsuit, similar to those worn by Guantanamo Bay inmates, and said he wanted to call on his family and friends to ‘rise up against my real killers, the US government’.

It is believed that IS had threatened to kill Mr Foley in retaliation for US air strikes on Mount Sinjar in northern Iraq, where militants have been making an advance in recent weeks.

Another US journalist, Steven Sotloff, was shown at the end of the video. He went missing near the Syria-Turkey border last year – and according to the IS fighter in the film, his life depends on Mr Obama’s ‘next decision’.

Nigel Farage, the leader of Ukip, has called on the government to stop Britons who have gone to fight for IS from returning. He added: ‘I would say that in choosing to fight abroad, they have rendered themselves effectively stateless by conforming to an ideology of wanting to create a terrifying caliphate.’